The invention relates to a coating agent based on self-emulsifying copolymers, particularly based on polyester oligomer polyacrylate and neutralising agent, and cross-linked with polyisocyanates and optionally containing conventional lacquer additives such as pigments, fillers and/or organic solvents. The aqueous coating agent is of use for producing lacquer coats, particularly for multilayer lacquer coats in the form of base lacquer, preferably clear lacquer, filler and/or coating lacquer.
The construction of multilayer lacquer coats is known particularly in the motor-vehicle construction industry. Advantageously a clear-lacquer layer is applied "wet-on-wet" on to a base lacquer layer after brief drying, followed by simultaneous final setting.
The earlier, not previously-published German Patent Application P 42 23 183.3 describes aqueous emulsions based on acrylic copolymers which are synthesised in one or more low-molecular polyesters and then cross-linked with a mixture of melamine resins and masked polyisocyanates.
It is also known to use unmasked polyisocyanate compounds in an aqueous medium. For example, EP-A-0 358 979, DE-A-4 101 696 and DE-A-3 829 589 describe aqueous dispersions of polyhydroxy acrylate resins in which any "lacquer polyisocyanates" can be emulsified.
EP-A-0 496 205 describes an aqueous dispersion of a hydroxyfunctional polyester resin in which any polyisocyanate can be emulsified.
EP-A-0 206 059, EP-A-0 081 628, EP-A-0 310 345 and EP-A-0 019 844 describe emulsifiers for polyisocyanates and in the form of reaction products of polyisocyanates with hydrophilic polyalkylene ether alcohols. The aqueous polyisocyanate emulsions are used as accelerators for aqueous adhesives or moulded members.
DE-A-41 37 429 describes aqueous binder combinations containing a polyol component consisting of a mixture of at least two polyester resins, one optionally being an acrylate-grafted polymer resin. Coating agents made therefrom have a strong tendency to turn yellow. EP-A-0 391 271 describes aqueous coating agents containing a water-soluble polyester oligomer polyacrylate and amine resin cross-linking agents.